c# 图文添加文字斜水印 优化

之前一篇给图片加水印的功能，加出来水印的图片位置有一点问题，并且如果图片分辨率有变动的话，水印会有层次不齐的问题。

目前只能优化到增加一条居中显示的斜水印，在不同分辨率不同大小的图片中，都能保证文字水印的字体大小从左下至右上能撑满整张图片。

思路是：先生成一张文字水印图片的PNG图片。

在你需要添加水印的图片上，把之前加的水印图片贴上去就可以了。

核心代码：

     //新建原始普通大小的bmp
     Bitmap bmCanvas = new Bitmap(imgSrc.Width, imgSrc.Height, PixelFormat.Format24bppRgb);
     Graphics gCanvas = Graphics.FromImage(bmCanvas);
     gCanvas.Clear(Color.White);
     gCanvas.SmoothingMode = SmoothingMode.HighQuality;
     gCanvas.InterpolationMode = InterpolationMode.High;
     //将原始图片加载入画布
     gCanvas.DrawImage(imgSrc, , , imgSrc.Width, imgSrc.Height);
     //计算图片对角线长度
     double diagonal = Math.Sqrt(Math.Pow(width, ) + Math.Pow(height, ));

     //计算对角线倾角
     double angle = Math.Asin(height / Math.Sqrt(Math.Pow(width, ) + Math.Pow(height, ))) / Math.PI * ;

     // 确定水印文字的字体大小
     int[] sizes = new int[]
     {
         , , , , , , , , , , , , , , , , , , ,
         , , , , , , , , , , , , , , , , , , ,
         , , , , , , , , , , , , , , , , , , , , , ,
         , , , , , , , , ,
     };
     Font crFont = null;
     SizeF crSize = new SizeF();

     for (int i = ; i < sizes.Length; i++)
     {
         crFont = new Font("微软雅黑", sizes[i], FontStyle.Bold);
         crSize = gCanvas.MeasureString(watermarkText, crFont);
         if ((int)crSize.Width < (int)diagonal * 0.9)
         {
             break;
         }
     }
     // 生成水印图片（将文字写到图片中）
     //Bitmap bmWaterMark = new Bitmap((int)crSize.Width + 3, (int)crSize.Height + 3, PixelFormat.Format32bppArgb);
     Bitmap bmWaterMark = new Bitmap(width, height, PixelFormat.Format32bppArgb);
     Graphics gWaterMark = Graphics.FromImage(bmWaterMark);

     gWaterMark.TranslateTransform(width / , height / );
     gWaterMark.RotateTransform(-(int)angle);
     gWaterMark.TranslateTransform(-crSize.Width / , -crSize.Height / );

     PointF pt = new PointF(, );
     // 画阴影文字
     Brush transparentBrush0 = new SolidBrush(Color.FromArgb(, Color.Black));
     Brush transparentBrush1 = new SolidBrush(Color.FromArgb(, Color.Black));
     gWaterMark.DrawString(watermarkText, crFont, transparentBrush0, pt.X, pt.Y + );
     gWaterMark.DrawString(watermarkText, crFont, transparentBrush0, pt.X + , pt.Y);
     gWaterMark.DrawString(watermarkText, crFont, transparentBrush1, pt.X + , pt.Y + );
     gWaterMark.DrawString(watermarkText, crFont, transparentBrush1, pt.X, pt.Y + );
     gWaterMark.DrawString(watermarkText, crFont, transparentBrush1, pt.X + , pt.Y);
     transparentBrush0.Dispose();
     transparentBrush1.Dispose();

     // 画文字
     gWaterMark.SmoothingMode = SmoothingMode.HighQuality;
     //Brush SolidBrush3 = new SolidBrush(Color.White);
     Brush solidBrush3 = new SolidBrush(Color.FromArgb(, Color.White));
     gWaterMark.DrawString(watermarkText, crFont, solidBrush3, pt.X, pt.Y, StringFormat.GenericDefault);
     solidBrush3.Dispose();

     // 保存刚才的操作
     gWaterMark.Save();
     gWaterMark.Dispose();
     bmWaterMark.Save(_wmImgSavePath, ImageFormat.Jpeg);

     //// 将水印图片加到原图中
     //AddWatermarkImage(gCanvas, new Bitmap(bmWaterMark), "WM_TOP_LEFT", width, height);

     using (var imageAttr = new ImageAttributes())
     {
         ColorMap colorMap = new ColorMap();
         colorMap.OldColor = Color.FromArgb(, , , );
         colorMap.NewColor = Color.FromArgb(, , , );
         ColorMap[] remapTable = { colorMap };
         imageAttr.SetRemapTable(remapTable, ColorAdjustType.Bitmap);
         float[][] colorMatrixElements =
         {
             new float[] {1.0f, 0.0f, 0.0f, 0.0f, 0.0f},
             new float[] {0.0f, 1.0f, 0.0f, 0.0f, 0.0f},
             new float[] {0.0f, 0.0f, 1.0f, 0.0f, 0.0f},
             new float[] {0.0f, 0.0f, 0.0f, 0.3f, 0.0f},
             new float[] {0.0f, 0.0f, 0.0f, 0.0f, 1.0f}
         };
         ColorMatrix colorMatrix = new ColorMatrix(colorMatrixElements);
         imageAttr.SetColorMatrix(colorMatrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
         gCanvas.DrawImage(bmWaterMark, new Rectangle(, , bmWaterMark.Width, bmWaterMark.Height), , ,
             bmWaterMark.Width, bmWaterMark.Height, GraphicsUnit.Pixel, imageAttr);
         gCanvas.Dispose();
     }
     bmWaterMark.Dispose();

代码已上传至GitHub，地址：https://github.com/hano7758/WaterMark